In this work, measurements from Cathodo-Luminescence (CL), micro-Raman spectroscopy and Breakdown Voltage (BV) have been coupled to assess the effects of physical parameters such as threading dislocations and effective doping level homogeneity on the electrical performances of vertical GaN Schottky and PN diodes. Two different substrates from Saint Gobain Lumilog and Sumitomo Electric with different threading dislocation densities have been compared